JPH0784123B2 - Damping force control device for shock absorber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention reduces the acceleration received by a vehicle body while the vehicle is traveling by controlling the damping force of the shock absorber according to the magnitude of the expansion and contraction acceleration of the shock absorber. , A shock absorber damping force control device for improving riding comfort.

[Conventional technology]

Conventionally, damping force control of a variable damping force type shock absorber is performed by estimating the running state (posture) of the vehicle by detecting the vehicle speed, throttle opening, steering angle, braking, etc. with many sensors. Due to its lack of accuracy, it has some effect when starting, stopping, or traveling at high speed, but it is still not sufficient to improve riding comfort during general driving.

In order to improve the riding comfort of the vehicle, it is sufficient to reduce the magnitude of the force applied to the vehicle body, that is, the acceleration applied to the vehicle body.
For that purpose, it is necessary to control the damping force of the shock absorber according to the unevenness of the road surface. Although only a few recently,
A method of detecting irregularities on the road surface using ultrasonic waves has been devised, but it has the drawbacks that the cost is high and the detection function is deteriorated due to dirt such as mud splashes.

[Problems to be solved by the invention]

The present invention has been made in view of the above problems, and an object thereof is to detect the movement of a wheel due to unevenness of the road surface from the expansion and contraction acceleration of the shock absorber when the vehicle is running, and to reduce the damping force of the shock absorber. It is to provide a shock absorber damping force control device that suppresses the acceleration applied to the vehicle body and minimizes the ride comfort by controlling according to the expansion and contraction acceleration.

[Means for solving problems]

According to the study by the present inventors, it was found that the damping force of the shock absorber becomes a comfortable riding force when switching control is performed based on the vibration frequency applied to the vehicle or the shock absorber from the road surface. However, this vibration frequency can be detected only after the wheel has passed through the unevenness of the road surface. Therefore, if the damping force is controlled by this, it will actually be slow.

Therefore, as a result of further study by the present inventors, it was found that there is a correlation between the vibration frequency from the road surface and the expansion / contraction acceleration of the shock absorber, and the present invention is based on the acceleration of the stroke displacement amount. The damping force is switched and controlled. Therefore, the present invention provides a damping force variable shock absorber capable of switching the damping force in at least two stages, a stroke sensor for detecting a stroke displacement amount of the shock absorber, and the shock absorber based on the displacement amount from the streak sensor. When the expansion / contraction acceleration is smaller than the preset acceleration, the damping force of the shock absorber is increased to be larger than the preset acceleration. The gist is that a damping force control means for switching the damping force of the shock absorber is provided so as to reduce the damping force when it is large.

[Action]

According to the above configuration of the present invention, when the shock absorber tries to pass through the unevenness of the road surface, the stroke displacement amount is detected by the stroke sensor, and the extension / contraction acceleration is obtained by the extension / contraction acceleration calculation means from the stroke displacement amount. When the expansion / contraction acceleration is smaller than the preset acceleration, the damping force of the shock absorber is increased,
When the acceleration is larger than the set acceleration, the damping force of the shock absorber is controlled to be small.

〔The invention's effect〕

According to the shock absorber damping force control device of the present invention, since the stroke displacement amount and the expansion / contraction acceleration of the shock absorber that change corresponding to the unevenness of the road surface are used, the road surface condition is detected using ultrasonic waves as in the conventional device. Since it is not necessary to use a sensor, it is not necessary to consider the mud splash adhered to the ultrasonic sensor, which is an excellent effect in practical use.

Further, the preset acceleration and the expansion / contraction acceleration obtained from the stroke displacement amount of the shock absorber are compared. When the expansion / contraction acceleration is smaller than the set acceleration number, the damping force of the shock absorber is large and is larger than the set acceleration. At this time, by switching the damping force of the shock absorber so as to reduce the damping force, the vibration transmitted from the road surface can be effectively suppressed in the entire frequency range.

〔Example〕

Hereinafter, a shock absorber damping force control device according to an embodiment of the present invention will be described with reference to the drawings. Before that, first, the relationship between the characteristics of the shock absorber and the riding comfort of the vehicle is clarified.

FIG. 2 is a diagram showing a model of the vehicle. 100 is an unsprung load (W1) such as a body supported by a suspension such as a shock absorber, 111 is an unsprung load (W2) such as an axle between the tire and the suspension spring, 112 is a suspension spring with a spring constant K1, 114 is a shock absorber having a damping coefficient C, and 113 is a wheel having a spring constant K2. 115 indicates a road surface.

In this model, the "comfort" actually felt by the driver or the passenger is closely related to the acceleration applied to the sprung load 100 of the vehicle body. Therefore, using this model, we will investigate the relationship between the unevenness of the road surface and the acceleration applied to the sprung load 100. In FIG. 2,
X represents the amount of displacement of the sprung load 100, Y represents the amount of displacement of the unsprung load 111, and Z represents the change of the road surface 115. Sinusoidal road surface 115
When the ratio G / A of the acceleration G applied to the vehicle body and the amplitude A of the road surface when the vehicle is driven is taken and the frequency F of road surface vibration is taken on the vertical axis, the result is as shown in FIG. That is, the shorter the vibration cycle F, the larger the acceleration applied to the vehicle body, and the riding comfort deteriorates. This shows almost the same result regardless of the magnitude of the amplitude A. The two peaks in the figure are considered to be resonance points, the low frequency is the sprung resonance, and the high frequency is the unsprung resonance, and the acceleration applied to the vehicle body increases.

Next, FIG. 4 shows the results when the damping force coefficient C of the shock absorber is increased to increase the damping force (two-dot chain line i) and when it is reduced (one-dot chain line ii). The acceleration received by the vehicle body is smaller when the damping coefficient C is larger at a frequency than a certain frequency Fs, and conversely when the reduction coefficient is small at a higher frequency. As a result, if the shock absorber is harder at a frequency lower than the frequency Fs near the spring resonance point and softer at a higher frequency than the intermediate hardness shown by the broken line in the figure, the acceleration applied to the vehicle body in all regions will be increased. It can be seen that the size can be reduced and the riding comfort can be improved.

However, if this vibration frequency is to be detected based on the vibration of the road surface, the wheel cannot detect this frequency unless it passes through the unevenness of the road surface once. This means that the damping force cannot be changed with respect to the unevenness of the road surface that is going to pass.

Therefore, the present inventors examined obtaining a control signal corresponding to the above frequency from the amount of displacement of the stroke of the shock absorber, and FIG. 5 shows the examination result. FIG. 5 shows the expansion / contraction displacement of the shock absorber with respect to the road vibration frequency, its acceleration, and its acceleration. In this case, the road surface amplitude A is set to 12.5 mm. From FIG. 5, the expansion and contraction displacements and expansion and contraction speeds of the shock absorber take a maximum at the resonance point, while the expansion and contraction acceleration uniformly increases with the increase in frequency near the sprung resonance point. Therefore, the expansion / contraction acceleration of the shock absorber is an effective clue for determining the vibration frequency Fs at which the damping force of the shock absorber needs to be switched. Here, if the road surface vibration amplitude is 12.5 mm and the switching set frequency is, for example, 1.2 hertz, the shock absorber expansion / contraction acceleration should be switched at 0.2 G.

FIG. 6 shows the relationship between the road surface amplitude A and the absorber expansion / contraction acceleration G. It indicates that the expansion / contraction acceleration of the absorber changes depending on the road surface amplitude, or conversely if the amplitude is small, the influence on the vehicle body is small unless the frequency becomes large. Therefore, the expansion / contraction acceleration of the shock absorber to be switched may be set according to the amplitude and frequency of the road surface that are considered to affect the vibration of the vehicle body.

Based on the above idea, the first embodiment of the present invention,
Shown in the figure. In FIG. 1, 130 is a shock absorber, 1
31 is a device that detects the expansion and contraction stroke of the shock absorber and issues a displacement signal, 124 and 125 are differentiating circuits, 123 is a device that processes the signal from the shock absorber and issues a damping force switching signal, 120 is another sensor such as a vehicle speed sensor , 121 is a circuit that comprehensively controls the damping force of the shock absorber, and 122 is a circuit that drives an actuator such as a motor that switches the damping force.

In the signal processing diagram shown in FIG. 1, the expansion / contraction acceleration of the shock absorber for switching the damping force of the shock absorber is set based on the constituent elements of the vehicle shown in FIG. In this case, when explaining an ordinary passenger car, 4
The spring load (W1), unsprung load (W2), spring constant (K1), and wheel spring constant (K2) acting on one of the shock absorbers are:
W1 = 400kg, W2 = 30kg, K1-2.0kg / mm, K2 = 25kg / mm respectively. Under these conditions, the vibration frequency Fs of the road surface when the damping force of the shock absorber is switched to 1/3 or 3 times is set to 1.2 Hz, and the expansion / contraction acceleration of the shock absorber at this time is set to 0.2 G. The damping force of the shock absorber is a value when the damping force of a normal shock absorber is set to 1.

Next, the operation of this device will be described. Here, description of control by signals from other sensors shown by 120 in FIG. 1 is omitted.

When the vehicle starts to move, the stroke detection device 131 converts the stroke displacement amount of the shock absorber 130 into an analog signal and enters the differentiating circuit 1125 to generate the expansion / contraction speed signal. Further, the differentiating circuit II124 produces the expansion / contraction acceleration signal. Based on these signals, the signal processing circuit 123 decreases the damping force (soft) when the expansion / contraction acceleration of the shock absorber is larger than the set value 0.2 G, and increases the damping force (hard) when the expansion / contraction acceleration is small. A control signal for switching the damping force to is issued. Therefore, the damping force is controlled largely under normal road conditions, but when the wheel bumps into the unevenness from the road surface, the damping force of the shock absorber is instantly controlled to be small due to the expansion and contraction of the wheel, so the unevenness of the road surface may be felt. Since the shock absorber is absorbed, riding comfort is improved.

Here, an example of the case of controlling in consideration of signals from other sensors will be described. The signal processing circuit of the signal processing circuit 123 is a comparator circuit shown in FIG. 7, and the set value of the shock absorber expansion / contraction acceleration is set to the vehicle speed. It is also possible to change according to. Furthermore, it is of course possible to detect braking, cornering, etc. by another sensor and switch the damping force regardless of the condition of the road surface.

The effect of the above control is to suppress a large fluffy vibration on a road surface with a large swell, and when a sudden protrusion is overriding, soften the thrust when riding and suppress the thrust.
After getting over, it will be stiff and hold back. On a rough road with a high vibration frequency as a whole, the car body can be stabilized by pushing softly and pushing up. The effect of the control according to this embodiment is shown in FIG. It can be seen that the acceleration applied to the vehicle body is reduced over almost the entire area compared to the conventional one. FIG. 9 shows the case where the damping force of the acceleration applied to the vehicle body is not controlled when the vehicle runs on a road surface having random unevenness (dotted line).
And a case of controlling by the device according to the present invention (solid line). Incidentally, Z indicates the change of the road surface. From this result, it is clear that the damping force control of the shock absorber according to the present invention reduces the acceleration applied to the vehicle,
It has a great effect on improving riding comfort. Next, the structure of a suitable shock absorber will be described using the control circuit described above.

FIG. 10 shows a vehicle suspension device provided with the displacement detecting device according to the present invention. The figure shows a suspension type suspension device having a shock absorber 130 with a variable damping force. The lower end of a cylinder 41 of the shock absorber 130 is fixed to an axle P and a piston rod protruding from the cylinder 41.
The upper end of 42 is connected to the body Q via a bearing 51 and a vibration-proof rubber 52 mounted on the outer circumference of the upper end. Also,
Spring receivers 43, 44 are provided at the upper ends of the cylinder 41 and the piston rod 42, respectively, and the suspension spring 6 is arranged between them.

A piston 45 that slides in the cylinder 41 is fixed to the lower end of the piston rod 42, and the piston 45 has throttle holes 451 and 452.
Is formed. A large-diameter cylindrical body is provided directly above the piston 45 fixing portion of the piston rod 42, and a piezo stack 46 and a spool valve 47 are arranged inside to face each other via a pressure chamber 48. The spool valve 47 is moved up and down as the piezo stack 46 expands and contracts, and opens and closes a liquid flow passage 49 formed in the piston rod 42 and connecting the upper and lower liquid chambers R and S.
The piezo stack 46 is controlled based on a signal from the damping force variable drive circuit 22. With such a structure, the liquid flow passage 49
When the valve is closed, the damping force of the shock absorber 4 increases.
Electromagnetic coils 1A and 1B serving as a stroke sensor 131 are provided at the upper ends of the spring receiver 43 and the cylinder 41 which face each other. The electromagnetic coil 1A is embedded in the insulating resin 11 fixed to the lower surface of the spring receiver 43, and the piston rod 42
It is concentrically arranged around this. The electromagnetic coil 1B is embedded concentrically with the piston rod 42 in the insulating resin 12 fixed to the outer periphery of the upper end of the cylinder 41. The coil 1A is connected to an exciting circuit 2 which is also embedded in the resin 11, and a lead wire 21 extending from the exciting circuit 2 to an external power source (not shown) is extended. The tip of the lead wire 21 serves as a connector 22. The electromagnetic coil 1B is connected to the detection circuit 3 embedded in the resin 12, and a lead wire 31 having a connector 32 at its tip is extended from the detection circuit 3. The lead wire 31 reaches the damping force control device shown in FIG. In the figure, 7 is a rubber stopper.

A sine wave exciting current is output from the exciting circuit 2, and the electromagnetic coil 1A to which the exciting current is input forms an alternating magnetic field in the surroundings, whereby an induced voltage is generated in the electromagnetic coil 1B. The induced voltage V at this time is expressed by the following equation.

Here, dI / dt is the amount of change in the exciting current, and M ₁₂ is the mutual inductance between the electromagnetic coils 1A and 1B. As is clear from the above equation, the induced voltage V is the mutual inductance M
The mutual inductance M ₁₂ is proportional to ₁₂ and changes according to the distance between the coils 1A and 1B. When the shock absorber 4 expands and contracts due to a change in the relative distance between the axle P and the body Q due to vibration input or the like, the electromagnetic coils 1A and 1B are expanded.
The mutual inductance between them changes accordingly, and the relative displacement of the shock absorber 4 on the axle side and the body side can be detected by the magnitude of the induced voltage V generated in the electromagnetic coil 1. The detection circuit 3 uses this electromagnetic coil 1B
DC detection voltage corresponding to the amplitude of the induced voltage generated in
That is, a stroke signal indicating displacement of the suspension is output. In the present embodiment, the electromagnetic coils 1A, 1B described above are used.
The diameter was 70 mm, the number of turns was 400, and the frequency of the excitation voltage was 1 KHz.

By using the piezo stack 4b for the spool valve 47 that opens and closes the liquid flow passage 49 that connects the upper and lower liquid chambers R and S of the shock absorber 130, the responsiveness is improved.
Further, as compared with the conventional motor type and the like, use of the piezo stack can provide a shock absorber having an extremely fast switching speed for damping force control.

Next, the structure of another form of shock absorber will be described with reference to FIG. Since the stroke sensor is the same as the shock absorber shown in FIG. 10 when the expansion and contraction stroke of the shock absorber is detected, it is omitted.

Upper and lower liquid chambers R and S defined by a piston 71 in a cylinder 70 of the shock absorber communicate with each other via a fixed throttle 72. The liquid chamber S communicates with the chamber 90 via the piston rod 73, the flexible pipe 74, and the passages 85 and 86 of the piezo stack valve 80. The chamber 90 contains an inert gas
90a is enclosed. In the piezo stack valve R, a piezo stack 81 and a spool valve 82 are arranged inside to face each other via a pressure chamber 83. The spool valve 82 is a piezo stack 8 controlled based on a signal from the damping force variable drive circuit 122.
The valve body 84 is moved up and down with the expansion and contraction of 1.
The passage 85 formed therein is opened and closed.

In the above configuration, when the passage 85 is closed by the spool valve 82, the damping force of the shock absorber increases, and the spring constant at this time is determined by the gas pressure of the gas 90a in the chamber 90. The control of the damping force is the same as that described above.

Incidentally, a microcomputer or the like may be used instead of the control circuit shown in FIG. 1 to perform similar control.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a schematic diagram modeling a vehicle suspension, and FIG.
Fig. 4 is a characteristic diagram showing the relationship between the frequency of road surface vibration and the acceleration applied to the vehicle when a conventional shock absorber is used in the motel shown in Fig. 4. Fig. 4 shows the road surface vibration when the damping force of the shock absorber is increased and when it is decreased. Showing the relationship between the frequency and the acceleration applied to the vehicle, FIG. 5 shows the relationship between the frequency of the road surface vibration and the shock absorber expansion / contraction displacement, speed and acceleration, and FIG. 6 shows each amplitude of the road surface vibration (A). Shows the relationship between the frequency of road surface vibration and the expansion / contraction acceleration of the shock absorber, FIG. 7 is a partial circuit diagram showing an example of the signal processing circuit of FIG. 1, and FIGS. 8 and 9 show the effects of the present invention. In the graph shown, FIG. 8 shows the relationship between the frequency of road surface vibration and the acceleration received by the vehicle, and FIG. 9 shows the relationship between the road surface state (Z) and the acceleration received by the vehicle. First
FIG. 10 is a block diagram showing the structure of a shock absorber suitable for applying the damping force control device of the shock absorber of the present invention, and FIG. 11 is a block diagram of the shock absorber showing another embodiment. 121 …… Damping force control circuit, 122 …… Damping force variable mechanism drive circuit, 123 …… Signal processing circuit, 124,125 …… Differential circuit that serves as expansion / contraction acceleration calculation means for obtaining expansion / contraction acceleration of shock absorber, 130 …… Damping force variable Shock absorber, 131 …… Shock absorber stroke sensor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-1520 (JP, A) JP-A-62-74705 (JP, A) JP-A-57-182506 (JP, A)

Claims (2)

[Claims] 1. A damping force variable shock absorber capable of switching the damping force in at least two stages, a stroke sensor for detecting a stroke displacement amount of the shock absorber, and a shock absorber of the shock absorber based on a displacement amount from the stroke sensor. Expansion / contraction acceleration calculating means for obtaining expansion / contraction acceleration, and comparing the expansion / contraction acceleration with a preset acceleration,
Damping force control means for switching the damping force of the shock absorber so as to increase the damping force of the shock absorber when the expansion / contraction acceleration is smaller than the set acceleration and to decrease the damping force when the expansion acceleration is larger than the set acceleration. A shock absorber damping force control device characterized by being provided. 2. The damping force control for a shock absorber according to claim 1, wherein the set acceleration is variably set to be small when the vehicle speed is low and to be large when the vehicle speed is high. apparatus.